1. Field of the Invention
This invention relates to bonded storage disks and, more particularly, to improved methods of and systems for forming bonded storage disk, such as digital versatile disks ("DVDs").
2. Discussion of Related Art
Two popular forms of storage media are compact disks ("CDs") and digital versatile disks ("DVDs") DVD is a form of a bonded storage disk. A bonded storage disk has two or more substrates held together by a cured bonding agent. At least one of the substrates is formed to have "pits," the distribution of which is representative of the information to be stored on the disk. These pits are metallized so that when they are "hit" by an optical signal they will reflect a signal indicative of the pit and thus the information.
Because of their ability to store vast amounts of information, DVDs have been well received in the market. To date, there are four specified DVD formats: DVD5, DVD9, DVD10, and DVD18. DVD5 is a single-sided, single-layered format (see FIG. 1C); DVD9 is a single-sided, dual layered form (see FIG. 1E); DVD10 is a dual-sided, single-layered format (see FIG. 1D); and DVD18 is a dual-sided, dual-layered format (see FIG. 1F). "Single-sided" means that the disk is intended to be read from one side only. "Dual-sided" means that the disk may be read from either side, with each side storing information. "Single-layered" means that for a given side there is one "layer" of information only. In this regard, a layer of information would mean a distribution of metallized pits 4, which when hit with a light source 9 will reflect an information-carrying optical signal. "Dual-layered" means that for a given side there are two layers 4 of information. The specifications are provided in the DVD Book, v. 1.0, by the DVD Forum, which is hereby incorporated by reference in its entirety. The Figures are not to scale. For example, in actuality the substrate 6 is about 0.6 mm thick; for DVD9 the bonding layer 8 is about 50 microns thick.+-.15 microns, .+-.10 microns within a DVD, and .+-.4 microns within a revolution; and the metallization layer 4 is on the order of tens of nanometers.
The formats specify several characteristics of a disk. For example, referring to FIGS. 1A-F, which show a plan view of a DVD and a cross-section view of DVD5, DVD9, DVD10, and DVD18 formats, the formats specify the inner diameter of the center hole, the outer diameter of the DVD, the handling area, the inner mirror band, the data area, and the outer mirror band. They also specify the shape and location of a stacking ring, the pit size, the reflectivity of the metal layers and the type of the metal, and for some formats the thickness and optical characteristics of the bonding agent used to form bond layer 8. In addition, the specifications list acceptable tolerances of certain "bulk parameters," such as "radial tilt" and "tangential tilt." The specifications also specify the thickness of the bonding layer and the acceptable amounts of bubbles and contaminants.
On the other hand, some aspects are undefined. For example, commercially-available substrate molding machines produce substrates having machine-specific moat locations and shapes. These moats are a consequence of a molding machine piece known as a "stamper holder." The stamper holder is a removable tool that is part of the mold and is used to hold the "stamper" in place. In the art, for example, there are known 22 mm moat geometries and 34 mm moat geometries. The 22 mm and 34 mm designations refer to the outer diameters of the moats. The moat is an artifact of the process and is not a design aspect with an intended function. In addition, though the reflectivity of the metal layers is specified (sometimes by minimums, other times by minimums and maximums) the actual amount of metallization is not.
To date, manufacturing DVDs has been problematic, especially for dual-layer formats and especially for achieving desirable yields. In part this is the result of the extremely tight manufacturing tolerances specified by the formats and required by the market. In other part this is due to the complexities introduced with the dual-layer arrangements having the bonding layer be an optical component of a DVD.
One of the problems affecting yields is the difficult in forming bonding layers. Consequently, there is a need in the art for a system, method and substrate that facilitates the formation of satisfactory bonding layers.